http://d.puremagic.com/issues/show_bug.cgi?id=1861

           Summary: .sort fails if opCmp takes ref param
           Product: D
           Version: 1.027
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: wbaxter@gmail.com


------
module opcmpref;
import std.stdio;
struct Pair
{
    int a, b;
    // Sort by b first then a
    //  Sorting fails if rhs is a 'ref' param.  Ok if ref removed.
    int opCmp(ref Pair rhs) {
        if (b!=rhs.b) return b-rhs.b;
        return a-rhs.a;
    }
    string toString()
    {
        return std.string.format("(%s,%s)",a,b);
    }
}
void main()
{
    // Single comparisons are all fine
    assert( !(Pair(0,0)<Pair(0,0)) );
    assert( !(Pair(1,0)<Pair(0,0)) );
    assert( !(Pair(0,1)<Pair(0,0)) );
    assert( !(Pair(1,1)<Pair(0,0)) );
    assert(  (Pair(0,0)<Pair(1,0)) );
    assert( !(Pair(1,0)<Pair(1,0)) );
    assert( !(Pair(0,1)<Pair(1,0)) );
    assert( !(Pair(1,1)<Pair(1,0)) );

    assert(  (Pair(0,0)<Pair(0,1)) );
    assert(  (Pair(1,0)<Pair(0,1)) );
    assert( !(Pair(0,1)<Pair(0,1)) );
    assert( !(Pair(1,1)<Pair(0,1)) );
    assert(  (Pair(0,0)<Pair(1,1)) );
    assert(  (Pair(1,0)<Pair(1,1)) );
    assert(  (Pair(0,1)<Pair(1,1)) );
    assert( !(Pair(1,1)<Pair(1,1)) );

    // But sorting fails when opCmp takes 'ref' param
    auto p = [Pair(0,0), Pair(3,0), Pair(2,1), Pair(1,4)];
    p.sort;
    writefln("p=",p);
    assert(p[0] == Pair(0,0));
    assert(p[1] == Pair(3,0));
    assert(p[2] == Pair(2,1));
    assert(p[3] == Pair(1,4));
}
------------

This may be something in the low-level lib rather than the compiler per-se. I'm not sure about that.  I have tested and found that the error happens with both Phobos and Tango.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1861


bugzilla@digitalmars.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID




------- Comment #1 from bugzilla@digitalmars.com  2008-02-22 14:08 -------
According to http://www.digitalmars.com/d/arrays.html, the parameter to a struct's opCmp() must be S or S*, not ref S.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1861





------- Comment #2 from andrei@metalanguage.com  2008-02-22 14:15 -------
Also, sort in std.algorithm should work with predicates that take references.


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http://d.puremagic.com/issues/show_bug.cgi?id=1861


wbaxter@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |enhancement
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |
            Summary|.sort fails if opCmp takes  |make .sort not fail if opCmp
                   |ref param                   |takes ref param




------- Comment #3 from wbaxter@gmail.com  2008-02-22 16:19 -------
Ok, the documentation says either use Type or Type* for opCmp.  The .sort
property does in fact work with either.  The problem with just using Type* is
that it isn't called for regular struct comparisons like
   Type a,b;
   a<b

The problem with using just Type is that it makes sorting unnecessarily slow, since value arguments will have to be copied for every call of the comparison function.

It makes no sense not to allow ref.  This is exactly the kind of thing ref was meant for, where you want value semantics, but only want to pass a pointer around.

Interestingly, if you provide BOTH a Type* and a ref Type version of opCmp, then regular comparisons will use the ref version, and .sort will use the pointer version.

But it would be nicer if ref just worked.  I find it very surprising that it doesn't, and until it does I would suggest that the documentation be changed to say in very big bold letters that EVEN THOUGH REF MAY APPEAR TO WORK FOR SMALL TEST CASES IT IS NOT SUPPORTED AND WILL FAIL IF YOU TRY TO .sort.


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http://d.puremagic.com/issues/show_bug.cgi?id=1861


Yao Gomez <yao.gomez@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yao.gomez@gmail.com
            Version|1.027                       |D1
            Summary|.sort fails if opCmp takes  |(D1 only) .sort fails if
                   |a ref param                 |opCmp takes a ref param


--- Comment #4 from Yao Gomez <yao.gomez@gmail.com> 2012-02-05 01:01:46 PST ---
Marking this as D1 only, as the built-in, AA.sort method is going to be deprecated.

With a slight modification, your test example passes and prints the correct result with the std.algorithm.sort function (D2 only).

------
module opcmpref;

import std.stdio, std.algorithm;

struct Pair
{
    int a, b;
    // Sort by b first then a
    //  Sorting fails if rhs is a 'ref' param.  Ok if ref removed.
    int opCmp(ref Pair rhs) {
        if (b!=rhs.b) return b-rhs.b;
        return a-rhs.a;
    }
    @property string toString()
    {
        return std.string.format("(%s,%s)",a,b);
    }
}
void main()
{
    // Single comparisons are all fine
    assert( !(Pair(0,0)<Pair(0,0)) );
    assert( !(Pair(1,0)<Pair(0,0)) );
    assert( !(Pair(0,1)<Pair(0,0)) );
    assert( !(Pair(1,1)<Pair(0,0)) );
    assert(  (Pair(0,0)<Pair(1,0)) );
    assert( !(Pair(1,0)<Pair(1,0)) );
    assert( !(Pair(0,1)<Pair(1,0)) );
    assert( !(Pair(1,1)<Pair(1,0)) );

    assert(  (Pair(0,0)<Pair(0,1)) );
    assert(  (Pair(1,0)<Pair(0,1)) );
    assert( !(Pair(0,1)<Pair(0,1)) );
    assert( !(Pair(1,1)<Pair(0,1)) );
    assert(  (Pair(0,0)<Pair(1,1)) );
    assert(  (Pair(1,0)<Pair(1,1)) );
    assert(  (Pair(0,1)<Pair(1,1)) );
    assert( !(Pair(1,1)<Pair(1,1)) );

    auto p = [Pair(0,0), Pair(3,0), Pair(2,1), Pair(1,4)];
    std.algorithm.sort(p);
    // prints 'p=[(0,0), (3,0), (2,1), (1,4)]'
    writefln("p=%s",p);

    assert(p[0] == Pair(0,0));
    assert(p[1] == Pair(3,0));
    assert(p[2] == Pair(2,1));
    assert(p[3] == Pair(1,4));
}
------

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